Description

The fwprintf() function places output on the named output stream. The wprintf()
function places output on the standard output stream stdout. The swprintf() function
places output followed by the null wide-character in consecutive wide-characters starting at *s;
no more than n wide-characters are written, including a terminating null wide-character,
which is always added (unless n is zero).

Each of these functions converts, formats and prints its arguments under control
of the format wide-character string. The format is composed of zero or
more directives: ordinary wide-characters, which are simply copied to the output stream and conversion specifications,
each of which results in the fetching of zero or more arguments.
The results are undefined if there are insufficient arguments for the format.
If the format is exhausted while arguments remain, the excess arguments are evaluated
but are otherwise ignored.

Conversions can be applied to the nth argument after the format in
the argument list, rather than to the next unused argument. In this
case, the conversion wide-character % (see below) is replaced by the sequence
%n$, where n is a decimal integer in the range [1, NL_ARGMAX],
giving the position of the argument in the argument list. This feature
provides for the definition of format wide-character strings that select arguments in
an order appropriate to specific languages (see the EXAMPLES section).

In format wide-character strings containing the %n$ form of conversion specifications, numbered
arguments in the argument list can be referenced from the format wide-character
string as many times as required.

In format wide-character strings containing the % form of conversion specifications, each
argument in the argument list is used exactly once.

All forms of the fwprintf() functions allow for the insertion of a
language-dependent radix character in the output string, output as a wide-character value.
The radix character is defined in the program's locale (category LC_NUMERIC). In
the POSIX locale, or in a locale where the radix character is not
defined, the radix character defaults to a period ( . ).

Each conversion specification is introduced by the % wide-character or by the
wide-character sequence %n$, after which the following appear in sequence:

Zero or more flags (in any order), which modify the meaning of the conversion specification.

An optional minimum field width. If the converted value has fewer wide-characters than the field width, it will be padded with spaces by default on the left; it will be padded on the right, if the left-adjustment flag (-), described below, is given to the field width. The field width takes the form of an asterisk (*), described below, or a decimal integer.

An optional precision that gives the minimum number of digits to appear for the d, i, o, u, x, and X conversions; the number of digits to appear after the radix character for the a, A, e, E, f, and F conversions; the maximum number of significant digits for the g and G conversions; or the maximum number of wide-characters to be printed from a string in s conversions. The precision takes the form of a period (.) followed by either an asterisk (*), described below, or an optional decimal digit string, where a null digit string is treated as 0. If a precision appears with any other conversion wide-character, the behavior is undefined.

An optional length modifier that specifies the size of the argument.

A conversion specifier wide character that indicates the type of conversion to be applied.

A field width, or precision, or both, may be indicated by an
asterisk (*). In this case an argument of type int supplies the
field width or precision. Arguments specifying field width, or precision, or both
must appear in that order before the argument, if any, to be
converted. A negative field width is taken as a - flag followed by
a positive field width. A negative precision is taken as if the
precision were omitted. In format wide-character strings containing the %n$ form of
a conversion specification, a field width or precision may be indicated by the
sequence *m$, where m is a decimal integer in the range [1,
NL_ARGMAX] giving the position in the argument list (after the format argument) of
an integer argument containing the field width or precision, for example:

wprintf(L"%1$d:%2$.*3$d:%4$.*3$d\n", hour, min, precision, sec);

The format can contain either numbered argument specifications (that is, %n$ and
*m$), or unnumbered argument specifications (that is, % and *), but normally
not both. The only exception to this is that %% can be
mixed with the %n$ form. The results of mixing numbered and unnumbered
argument specifications in a format wide-character string are undefined. When numbered argument specifications
are used, specifying the Nth argument requires that all the leading arguments,
from the first to the (N-1)th, are specified in the format wide-character
string.

The flag wide-characters and their meanings are:

'

The integer portion of the result of a decimal conversion (%i, %d, %u, %f, %F, %g, or %G) will be formatted with thousands' grouping wide-characters. For other conversions the behavior is undefined. The non-monetary grouping wide-character is used.

-

The result of the conversion will be left-justified within the field. The conversion will be right-justified if this flag is not specified.

+

The result of a signed conversion will always begin with a sign (+ or -). The conversion will begin with a sign only when a negative value is converted if this flag is not specified.

space

If the first wide-character of a signed conversion is not a sign or if a signed conversion results in no wide-characters, a space will be prefixed to the result. This means that if the space and + flags both appear, the space flag will be ignored.

#

This flag specifies that the value is to be converted to an alternative form. For o conversion, it increases the precision (if necessary) to force the first digit of the result to be 0. For x or X conversions, a non-zero result will have 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g, or G conversions, the result will always contain a radix character, even if no digits follow it. Without this flag, a radix character appears in the result of these conversions only if a digit follows it. For g and G conversions, trailing zeros will not be removed from the result as they normally are. For other conversions, the behavior is undefined.

0

For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros (following any indication of sign or base) are used to pad to the field width; no space padding is performed. If the 0 and - flags both appear, the 0 flag will be ignored. For d, i, o, u, x, and X conversions, if a precision is specified, the 0 flag will be ignored. If the 0 and ' flags both appear, the grouping wide-characters are inserted before zero padding. For other conversions, the behavior is undefined.

The length modifiers and their meanings:

hh

Specifies that a following d, i, o, u, x, or X conversion specifier applies to a signed char or unsigned char argument (the argument will have been promoted according to the integer promotions, but its value shall be converted to signed char or unsigned char before printing); or that a following n conversion specifier applies to a pointer to a signed char argument.

h

Specifies that a following d, i, o, u, x, or X conversion specifier applies to a short or unsigned short argument (the argument will have been promoted according to the integer promotions, but its value shall be converted to short or unsigned short before printing); or that a following n conversion specifier applies to a pointer to a short argument.

l (ell)

Specifies that a following d, i, o, u, x, or X conversion specifier applies to a long or unsigned long argument; that a following n conversion specifier applies to a pointer to a long argument; that a following c conversion specifier applies to a wint_t argument; that a following s conversion specifier applies to a pointer to a wchar_t argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion specifier.

ll (ell-ell)

Specifies that a following d, i, o, u, x, or X conversion specifier applies to a long long or unsigned long long argument; or that a following n conversion specifier applies to a pointer to a long long argument.

j

Specifies that a following d, i, o, u, x, or X conversion specifier applies to an intmax_t or uintmax_t argument; or that a following n conversion specifier applies to a pointer to an intmax_t argument.

z

Specifies that a following d, i, o, u, x, or X conversion specifier applies to a size_t or the corresponding signed integer type argument; or that a following n conversion specifier applies to a pointer to a signed integer type corresponding to size_t argument.

t

Specifies that a following d, i, o, u, x, or X conversion specifier applies to a ptrdiff_t or the corresponding unsigned type argument; or that a following n conversion specifier applies to a pointer to a ptrdiff_t argument.

L

Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a long double argument.

If a length modifier appears with any conversion specifier other than as
specified above, the behavior is undefined.

The conversion wide-characters and their meanings are:

d, i

The int argument is converted to a signed decimal in the style [-]dddd. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeros. The default precision is 1. The result of converting 0 with an explicit precision of 0 is no wide-characters.

o

The unsigned int argument is converted to unsigned octal format in the style dddd. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeros. The default precision is 1. The result of converting 0 with an explicit precision of 0 is no wide-characters.

u

The unsigned int argument is converted to unsigned decimal format in the style dddd. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeros. The default precision is 1. The result of converting 0 with an explicit precision of 0 is no wide-characters.

x

The unsigned int argument is converted to unsigned hexadecimal format in the style dddd; the letters abcdef are used. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeros. The default precision is 1. The result of converting 0 with an explicit precision of 0 is no wide-characters.

X

Behaves the same as the x conversion wide-character except that letters “ABCDEF” are used instead of “abcdef”.

f, F

The double argument is converted to decimal notation in the style [-]ddd.ddd, where the number of digits after the radix character (see setlocale(3C)) is equal to the precision specification. If the precision is missing it is taken as 6; if the precision is explicitly 0 and the # flag is not specified, no radix character appears. If a radix character appears, at least 1 digit appears before it. The converted value is rounded to fit the specified output format according to the prevailing floating point rounding direction mode. If the conversion is not exact, an inexact exception is raised.

For the f specifier, a double argument representing an infinity or NaN is converted in the style of the e conversion specifier, except that for an infinite argument, “infinity” or “Infinity” is printed when the precision is at least 8 and “inf” or “Inf” is printed otherwise.

For the F specifier, a double argument representing an infinity or NaN is converted in the SUSv3 style of the E conversion specifier, except that for an infinite argument, “INFINITY” is printed when the precision is at least 8 and or “INF” is printed otherwise.

e, E

The double argument is converted in the style [-]d.ddde ± dd, where there is one digit before the radix character (which is non-zero if the argument is non-zero) and the number of digits after it is equal to the precision; if the precision is missing, it is taken as 6; if the precision is 0 and no # flag is present, no radix character appears. The converted value is rounded to fit the specified output format according to the prevailing floating point rounding direction mode. If the conversion is not exact, an inexact exception is raised. The E conversion wide-character will produce a number with E instead of e introducing the exponent. The exponent always contains at least two digits. If the value is 0, the exponent is 0.

Infinity and NaN values are handled in one of the following ways:

SUSv3

For the e specifier, a double argument representing an infinity is printed as “[-]infinity”, when the precision for the conversion is at least 7 and as “[-]inf” otherwise. A double argument representing a NaN is printed as “[-]nan”. For the E specifier, “INF“, “INFINITY”, and “NAN”are printed instead of “inf”, “infinity”, and “nan”, respectively. Printing of the sign follows the rules described above.

Default

A double argument representing an infinity is printed as “[-]Infinity”, when the precision for the conversion is at least 7 and as “[-]Inf” otherwise. A double argument representing a NaN is printed as “[-]NaN”. Printing of the sign follows the rules described above.

g, G

The double argument is converted in the style f or e (or in the style E in the case of a G conversion wide-character), with the precision specifying the number of significant digits. If an explicit precision is 0, it is taken as 1. The style used depends on the value converted; style e (or E) will be used only if the exponent resulting from such a conversion is less than -4 or greater than or equal to the precision. Trailing zeros are removed from the fractional portion of the result; a radix character appears only if it is followed by a digit.

A double argument representing an infinity or NaN is converted in the style of the e or E conversion specifier, except that for an infinite argument, “infinity”, “INFINITY”, or “Infinity” is printed when the precision is at least 8 and “inf”, “INF”, or “Inf” is printed otherwise.

a, A

A double argument representing a floating-point number is converted in the style “[-]0xh.hhhhp±d”, where the single hexadecimal digit preceding the radix point is 0 if the value converted is zero and 1 otherwise and the number of hexadecimal digits after it are equal to the precision; if the precision is missing, the number of digits printed after the radix point is 13 for the conversion of a double value, 16 for the conversion of a long double value on x86, and 28 for the conversion of a long double value on SPARC; if the precision is zero and the '#' flag is not specified, no decimal-point wide character appears. The letters “abcdef” are used for a conversion and the letters “ABCDEF” for A conversion. The A conversion specifier produces a number with 'X' and 'P' instead of 'x' and 'p'. The exponent always contains at least one digit, and only as many more digits as necessary to represent the decimal exponent of 2. If the value is zero, the exponent is zero.

The converted value is rounded to fit the specified output format according to the prevailing floating point rounding direction mode. If the conversion is not exact, an inexact exception is raised.

A double argument representing an infinity or NaN is converted in the SUSv3 style of an e or E conversion specifier.

c

If no l (ell) qualifier is present, the int argument is converted to a wide-character as if by calling the btowc(3C) function and the resulting wide-character is written. Otherwise the wint_t argument is converted to wchar_t, and written.

s

If no l (ell) qualifier is present, the argument must be a pointer to a character array containing a character sequence beginning in the initial shift state. Characters from the array are converted as if by repeated calls to the mbrtowc(3C) function, with the conversion state described by an mbstate_t object initialized to zero before the first character is converted, and written up to (but not including) the terminating null wide-character. If the precision is specified, no more than that many wide-characters are written. If the precision is not specified or is greater than the size of the array, the array must contain a null wide-character.

If an l (ell) qualifier is present, the argument must be a pointer to an array of type wchar_t. Wide characters from the array are written up to (but not including) a terminating null wide-character. If no precision is specified or is greater than the size of the array, the array must contain a null wide-character. If a precision is specified, no more than that many wide-characters are written.

p

The argument must be a pointer to void. The value of the pointer is converted to a sequence of printable wide-characters.

n

The argument must be a pointer to an integer into which is written the number of wide-characters written to the output so far by this call to one of the fwprintf() functions. No argument is converted.

C

Same as lc.

S

Same as ls.

%

Output a % wide-character; no argument is converted. The entire conversion specification must be %%.

If a conversion specification does not match one of the above forms,
the behavior is undefined.

In no case does a non-existent or small field width cause truncation
of a field; if the result of a conversion is wider than
the field width, the field is simply expanded to contain the conversion
result. Characters generated by fwprintf() and wprintf() are printed as if fputwc(3C) had
been called.

The st_ctime and st_mtime fields of the file will be marked for
update between the call to a successful execution of fwprintf() or wprintf()
and the next successful completion of a call to fflush(3C) or fclose(3C)
on the same stream or a call to exit(3C) or abort(3C).

Return Values

Upon successful completion, these functions return the number of wide-characters transmitted excluding
the terminating null wide-character in the case of swprintf() or a negative
value if an output error was encountered.

If n or more wide characters were requested to be written, swprintf()
returns a negative value.

Errors

For the conditions under which fwprintf() and wprintf() will fail and may
fail, refer to fputwc(3C).

In addition, all forms of fwprintf() may fail if:

EILSEQ

A wide-character code that does not correspond to a valid character has been detected.

EINVAL

There are insufficient arguments.

In addition, wprintf() and fwprintf() may fail if:

ENOMEM

Insufficient storage space is available.

Examples

Example 1 Print Language-dependent Date and Time Format.

To print the language-independent date and time format, the following statement could
be used:

wprintf(format, weekday, month, day, hour, min);

For American usage, format could be a pointer to the wide-character string:

L"%s, %s %d, %d:%.2d\n"

producing the message:

Sunday, July 3, 10:02

whereas for German usage, format could be a pointer to the wide-character
string: